The present invention relates to a dipole ion source. Before turning to the detailed description of the presently preferred embodiments, related prior art is discussed below. The related prior art is grouped into the following sections: extended acceleration channel ion sources, anode layer ion sources, Kaufman type ion sources, Penning discharge type ion sources, facing target sputtering, plasma treatment with a web on a drum, and other prior art methods and apparatuses.
Extended Acceleration Channel Ion Sources
Extended acceleration channel ion sources have been used as space thrust engines and for industrial ion sources for many years. The embodiments described in U.S. Pat. No. 5,359,258 to Arkhipov et al. are typical examples of these sources. These sources have a separate electron source to provide electrons to the ion source. Pole erosion is an issue with these sources.
Anode Layer Ion Sources
Anode layer ion sources (see U.S. Pat. No. 5,838,120 to Semenkin et al.) are another variation of ion source that places the anode to interrupt a portion of the electron containing magnetic field. These sources do not require a separate electron source. Recently, they have been commercialized for industrial use by Advanced Energy Industries, Inc. and other vendors. Similar to the extended acceleration channel sources, the substrate is placed outside the containing magnetic field, outside the gap between cathode surfaces.
Kaufman Type Ion Sources
Kaufman, working at NASA, developed this type of ion source to a high level in the early 1960's (see J. Reece Roth, Industrial Plasma Engineering, Volume 1: Principles, pp 200–204, IOP Publishing, Ltd. 1995). These sources place the substrate outside of the electron confining magnetic field.
Penning Discharge Type Ion Sources
Several variations of a Penning discharge type ion source are discussed in J. Reece Roth, Industrial Plasma Engineering, Volume 1: Principles, pp 204–208 and FIG. 9.31, IOP Publishing, Ltd. 1995.
Facing Target Sputtering
U.S. Pat. No. 4,963,524 to Yamazaki shows a method of producing superconducting material. An opposed target arrangement is used with the substrate positioned between the electrodes in the magnetic field. In this method, the magnetic field is symmetrical between the electrodes and the substrates are in the middle of the gap. When the substrates are placed in this position, the tall current generated within the magnetic field tends to be distorted and broken, and the plasma is extinguished and/or the voltage is much higher.
Plasma Treatment with a Web on a Drum
In U.S. Pat. Nos. 5,224,441 and 5,364,665 to Felts et al., a flexible substrate is disposed around an electrified drum with magnetic field means opposite the drum behind grounded or floating shielding. Magnetic field lines are not shown.
In U.S. Pat. No. 4,863,756 to Hartig et al., the substrate is continuously moved over a sputter magnetron surface with the surface facing the magnetron located inside the dark space region of the cathode. In this way, the magnetic field of the magnetron passes through the substrate and is closed over the substrate surface constricting the plasma onto the surface.
Other Prior Art Methods and Apparatuses
In U.S. Pat. No. 4,631,106 to Nakazato et al., magnets are located under a wafer to create a magnetron type field parallel to the wafer. The magnets are moved to even out the process. The opposed plate is grounded, and the wafer platen is electrified. U.S. Pat. No. 4,761,219 to Sasaki et al. shows a magnetic field passing through a gap with the wafer on one electrode surface. U.S. Pat. No. 5,225,024 to Hanley et al. has a mirror magnetic field where a cusp field is generated to create flux lines parallel to the wafer surface. In U.S. Pat. No. 5,437,725 to Schuster et al., a metal web is drawn over a drum containing magnets.